Action: Change tillage practices

Key messages

Biodiversity loss: Eleven studies from Canada, Europe, Mexico, or the USA measured effects of reduced tillage on soil animals or microbes. Of these, four (including three replicated trials (three also randomized and one also controlled)) found more microbes, more species of earthworm, or higher microbe activity under reduced tillage. One replicated trial found increased numbers of soil animals and earthworms under reduced tillage. One controlled, replicated trial found mixed effects on microbe diversity depending on time of sampling. Two, (including one controlled, replicated trial) found no effect of reduced tillage on earthworm activity or microbe activity.

Compaction: Five studies from Australia, Canada, and Europe measured the effect of controlled traffic and reduced tillage on compacted soils. Of these, two (including one before-and-after trial and one replicated trial) found reduced compaction and subsequent effects (reduced water runoff, for example) under controlled traffic, and one also found that crop yields increased under no-tillage. Three replicated trials, including one site comparison study, found higher compaction under reduced tillage.

Drought: Three replicated trials from Europe and India (one also randomized) found the size of soil cracks decreased, and ability of soil to absorb water and soil water content increased with conventional ploughing and sub-soiling.

Soil organic carbon: Twelve studies from Australia, Canada, China, Europe, Japan and the USA compared the effect of no-tillage and conventionally tilled systems on soil organic carbon. All (including two randomized, five replicated, two randomized, replicated, and one controlled, randomized, replicated) found higher soil organic carbon in soils under a no-tillage or reduced tillage system compared to conventionally tilled soil. One review showed that no-tillage with cover cropping and manure application increases soil organic carbon. One randomized, replicated trial from Spain found greater soil organic carbon in conventionally tilled soil. One replicated trial from Canada found no effect of tillage on soil carbon.

Soil organic matter: Fifteen studies from Canada, China, Europe, Morocco, and the USA measured effects of reduced tillage on soil organic matter content and nutrient retention. Of these, eight studies (including four replicated (two also randomized), two site comparisons (one also replicated) and one controlled) found maintained or increased soil organic matter and improved soil structure under reduced tillage. Four trials (including two replicated and two site comparison studies) found higher nutrient retention under reduced tillage. One controlled, replicated trial found less carbon and nitrate in no-till compared to conventionally tilled soil, but conventionally tilled soil lost more carbon and nitrate. One controlled, randomized, replicated trial and one replicated trial found mixed effects of reduced tillage on soil nitrogen levels.

Yield:One replicated study from Canada found lower yields under minimum or no-tillage compared to conventional tillage, and one controlled, randomized, replicated study from the USA found higher yields when subsoiling was done. One randomized, replicated study from Portugal found no effect of tillage treatment on yield.

There are several ways of tilling the soil in preparation for crop planting. Harrowing and ploughing are also known as conventional tillage. Harrowing is the disturbing or breaking up of soil using an agricultural implement with spike-like teeth (tines) or upright discs. Mouldboard ploughing involves using a plough that turns the soil. Both methods plough to 20 cm depth or more. Shallow tillage uses the same techniques as conventional tillage, but involves only tilling to 15 cm or less in depth. Conservation tillage comprises several methods of soil tillage which leave a minimum of 30% of crop residue on the soil surface. No-tillage involves direct drilling of crops straight into the soil, or leaving fields fallow without disturbing the soil.

Many different measures can be used to determine the health of the soil. Soil porosity is a measure of the volume of air in soil (an indicator of good soil structure, which tends to occur in healthy soils). Bulk density is a measure of the density of the soil. Unsaturated hydraulic conductivity is the ability of the soil to transmit water when a hydraulic (water) gradient is applied. Soil microbial biomass is the amount of tiny living organisms in a given amount of soil. Nematodes are tiny, often microscopic worms. Having high numbers of microbes or nematodes in the soil is generally an indicator of good soil health. Arbuscular mycorrhizal fungi are a group of fungi that live around the roots of plants. By living together, the fungi and host plant benefit each other: the fungi can live in a habitat without having to compete for resources and have a supply of carbon from the plant, while they provide an enhanced supply of nutrients to the plant, improving plant growth, the ability to reproduce and tolerance to drought. Arbuscular mycorrhizal fungi colonize a wide variety of host plants, including grasses, herbs, agricultural crops and legumes (Bardgett 2005).

Bardgett (2005) The Biology of Soil: A community and ecosystem approach. Oxford University Press, Oxford.

Supporting evidence from individual studies

1

A replicated experiment in 1970-1974 on sandy-clay to clay soil in Nigeria (Lal, 1976) found lower runoff under no-till maize Zea mays-cowpea Vigna unguiculata treatments (2% of total annual rainfall) compared to conventionally ploughed bare fallow (36%). Soil loss was lower under no-till (0.1 t/ha) compared to conventionally ploughed continuous maize (41 t/ha), cowpea-maize (43 t/ha) and bare fallow (230 t/ha) treatments. Slopes of 1, 5, 10 and 15% received the following treatments: bare fallow (conventionally ploughed); continuous maize (conventionally ploughed, mulched); continuous maize (conventionally ploughed, no mulch); maize-cowpea rotation (zero-tillage); and cowpeas-maize rotation (conventionally ploughed). Plots were 25 x 4 m and were replicated five times on each slope. Soil and runoff water was collected from each plot after every rainstorm using a water collection system below ground level downslope of the plots.

2

A replicated experiment in 1970-1974 on sandy-clay to clay soil in Nigeria (Lal, 1976), found lower nutrient loss in maize Zea mays-cowpea Vigna unguiculata under no-till (4.3 kg/ha)compared to conventionally ploughed cowpeas- maize (12 kg/ha), continuous maize (17 kg/ha) and bare fallow (55 kg/ha). Slopes of 1, 5, 10 and 15% received the following treatments: bare fallow (conventionally ploughed); continuous maize (conventionally ploughed, mulched); continuous maize (conventionally ploughed, no mulch); maize-cowpea rotation (zero-tillage); and cowpea-maize rotation (conventionally ploughed). Maize received 120, 26 and 60 kg/ha nitrogen, phosphorus and potassium respectively. Plots were 25 x 4 m and were replicated five times on each slope. Soil and runoff water was collected from each plot after every rainstorm using a water collection system below ground level downslope of the plots.

3

A site comparison study in 1989 on clay loam soils in north-central Italy (Mbagwu & Bazzoffi, 1989) found that conventional tillage decreased soil stability and organic matter content by 81.4 mg/kg compared to untilled plots. Soil density was slightly higher (by 0.018 g cm3) and the soil less porous (by 0.52%) under conventional tillage compared to not tilled or minimum tilled land. The experiment was carried out at three locations: Vicarello (soil not tilled and conventionally tilled), Fagna (soil minimal till, conventionally tilled), Gambassi (not tilled (alfalfa Medicago sativa pasture) and conventionally tilled). Plot size was not specified. Soil samples were collected at each location. The density of soil and the number of pores, as well as soil stability were measured.

4

A site comparison study in 1984-1987 on peat overlaying clay soil in Plynlimon, UK (Roberts et al. 1989) found that disc harrowing can cause large quantities of nitrate to be released (18.2 mg N/l) compared to reduced tillage (less than 1 mg N/l). There were two sites: (1) 1.5 ha of soft rush Juncus effusus and purple moor grass Molinia caerulaea. The area was disc harrowed, and lime, basic slag, fertilizer and a nitrogenous fertilizer were applied; (2) 19.5 ha area with purple moor grass and small areas of blanket mire Calluna vulgaris-Eriophorum vaginatum. Lime and phosphate fertilizer were applied, then grass seed was sown using the spike seeding method (a reduced tillage method - ground is spiked with a spike-aerator, then seed is broadcast over the soil). Soil and water samples were collected. Water flow, nitrate, phosphorus and potassium levels were measured.

5

A replicated experiment in 1985-1987 on loamy soil in Essonne, France (Balesdent et al. 1990) found that, soil organic carbon in wheat Triticum aestivum was higher under no-tillage (11.14 mg C/g) compared to conventional tillage (10.1 mg C/g). Superficial tillage was similar to conventional in the ploughed layer. In maize Zea mays, superficial tillage had higher soil organic carbon (9.88 mg C/g) compared to no-tillage (6.73 mg C/g) and conventional tillage (9.3 mg C/g). Average annual maize yields were 6.5 t/ha under conventional, 6.2 t/ha under superficial and 5.7 t/ha under no-tillage (wheat not reported). Crops were continuous wheat and maize. Three tillage treatments were applied to each crop in four replicates: conventional (ploughing to 30 cm, field cultivator), superficial (rotivator to 12 cm, field cultivator) and no-tillage (direct sowing). Plot size not specified. Soil samples were taken from 10 x 20 cm areas in each treatment, and carbon levels were measured using 13carbon.

A randomized replicated experiment in 1990-1991 on a calcareous silt loam soil in Shoreham, England, UK (Robinson & Naghizadeh, 1992) found that shallow cultivation reduces the amount of soil lost (4.53 g/h on average) and the amount of runoff (0.82 l/h on average) during heavier rainfall events compared to conventionally cultivated and rolled (with a heavy roller) land (25.54 g/h, 5.87 l/h on average, respectively). There were two sites with cultivated plots (number not specified), which were 100 x 18 m. Plots had three different cultivation practices (shallow cultivation, conventional deep cultivation, and deep cultivation followed by heavy rolling). A rainfall simulator was used, with each treatment subjected to three simulated rainfall events, lasting one hour at 42.5 mm/h. Runoff and eroded soil was caught in a trap in the slope immediately below the rainfall simulator. The volume of runoff and weight of eroded soil were measured.

8

A replicated experiment in 1992 on silt loam in Illinois, USA (Bradford and Huang, 1994) found decreased infiltration rates and increased soil loss under both no-till (from >70 to 47.1 mm/h and 0.01-0.15 kg/m2/h) and till (from 64.1 to 37.2 mm/h and 0.1-0.6 kg/m2/h respectively), when crop residue was removed. Removing residue from a no-till system increased soil loss at Site 2 from 0.01-0.13 kg/m2/h and Site 3 from 0.01-0.16 kg/m2/h. There were three sites under corn Zea mays-soybean Glycine max rotations. Site 1 was under conventional tillage and treatments were: tilled and tilled residue removed. Sites 2 and 3 had been no-till for more than 15 years. Site 2 treatments were: no-till, no-till residue removed, tillage residue replaced on surface, and tillage residue removed. Site 3 treatments were: no-till, no-till residue removed, tillage residue removed, and tillage residue removed again after three soil-drying days. Plots were 1 x 2 m and respective treatments were replicated six times at each site. Rainfall was simulated at an intensity of 70 mm/h on each plot for 90 minutes.

A site comparison study in 1981-1982 on clay-, silt- and sandy-loam and loam soils in Oklahoma and Texas, USA (Sharpley et al. 1995) found that total phosphorus loss was 93% lower from no-till soil than conventionally tilled soil. In no-till soil, 73% of the phosphorus was bioavailable (the point at which it becomes available for use after application) compared with 28% in conventionally tilled soil. At Bushland, the wheat Tiricum aestivum – sorghum Sorghum bicolor fallow rotation was under reduced tillage (stubble mulch tillage). At El Reno and Woodward, wheat was under conventional tillage/ploughing (chisel, mouldboard and discing). At Fort Cobb, the peanut Arachis hypogaea – sorghum rotation was under conventional tillage/ploughing (chisel, mouldboard, harrowing and discing). At each unfertilized and fertilized watershed, four soil samples were collected at monthly intervals. Runoff, total, organic and inorganic phosphorus were measured.

11

A replicated experiment in 1990-1991 on loamy sand in the USA (Torbert and Reeves, 1995) found that plant nitrogen uptake during the dry year was 27% lower under no-tillage compared to subsoiling. Plant nitrogen uptake during the wet year was higher under no traffic and tillage (186 kg N/ha) than when under combined traffic and tillage (161 kg N/ha). The experimental area was split into two with corn Zea mays planted in one half, and soybean Glycine Max. Treatments included: no-tillage, annual subsoiling (to 44 cm depth), and one-time complete disruption (subsoiling the middle 25cm of each strip plot). Plots were 21.3 x 6.1 m strips. Within each treatment, two further treatments were applied: no traffic, and traffic (plots driven over by a 4.6 Mg tractor). Within the traffic treatments were two residue management treatments: no-tillage and crop residue in corporation (using a disc). Nitrogen fertilizer was added to 2.3 x 1.8 m of each treatment. Soils were sampled to 90 cm depth.

12

A replicated experiment in 1990 on silty-clay soil near Stuttgart, Germany (Friedel et al. 1996) found that organic carbon, nitrogen and soil microbial activities in the topsoil were higher in rotary cultivated plots (1.6% C, 1.7 mg N/g, 6.8 μmol ATP/kg respectively) than under ploughing (1.3% C, 1.45 mg N/g, 4.5 μmol ATP/kg respectively). Below the topsoil, there was either no difference between tillage systems, or there was a marginal increase in the ploughed plots. There was an overlapping effect of cultivation and crop rotation on soil organic matter and microbial biomass. There were four replicates of two tillage treatments (ploughing to 25 cm; rotary cultivation 10-12 cm depth), and two crop rotations: legume/cereals (alfalfa Medicago sativa/wheat Triticum aestivum/oats Avena sativa/clover grass Trifolium spp.); rape Brassica napus/cereals (rape/wheat/oats/barley Hordeum vulgare). Plots were 15 x 6 m. Soil organic matter was added to the plots. Soil samples were collected to 25 cm depth. Enzyme activities, organic carbon, the potential for carbon and nitrogen mineralization and water-soluble carbon were measured.

A replicated experiment in 1982-1994 on silt loam (Delhi) and sandy loam (Elora) in Canada (Wanniarachchi et al. 1999) found no change in overall soil carbon under minimal and no-tillage compared to conventional tillage. Carbon from corn Zea mays made up 25-26% of total carbon at Delhi under minimum and conventional tillage, equivalent to 61-65 g C/m2/y. At Elora, carbon from corn made up 10% and 8.4% of total carbon under conventional and no-tillage respectively. Corn yield at Delhi was lower under no-tillage (7.1 Mg/ha/dry weight) compared to conventional (7.3 Mg/ha), and at Elora was lower under minimum (6.6 Mg/ha) compared to conventional tillage (6.9 Mg/ha). At Delhi there were two treatments under continuous corn Zea mays and tobacco Nicotiana tabacum-rye Secale cereale crops: conventional tillage (spring mouldboard ploughing to 15 cm depth followed by discing twice to 10 cm depth), and no-tillage. At Elora were two treatments under continuous corn: conventional (autumn mouldboard ploughing to 20 cm depth followed by secondary tillage with a field cultivator), and minimum tillage (autumn chisel ploughing to 12 cm depth and spring secondary tillage). There were four replicates. Plot size was not specified. Soils were sampled to 50 cm depth at both sites.

16

A randomized, replicated experiment in 1996-1998 on a sandy, silty and clay soil in Ludhiana, India (Jalota et al. 2001) found that tillage and straw mulching had no effect on soil water storage in the coarsest soil. Soil water content was higher in tilled soil (0.131 m3 water/m3) and soil with straw mulch (0.132 m3 water/m3 soil) relative to untreated and mulched soils (0.106 and 0.118 m3 water/m3) across all three soil types. Tillage did not increase soil water content to the same extent as straw mulch in coarse- to medium-textured soils. The study tested four treatments: untreated, tilled to 8 cm-depth, straw mulch (rice Oryza sativa in September and wheat Triticum aestivum in April) 6 t/ha, and straw incorporation. The treatments were replicated three times on each of three soil types in 2.5 x 3.5 m, 5 x 3 m, and 6 x 4 m plots. Mechanical weeding or herbicides (glyphosate) kept plots weed free. Soil water content was measured every 15-20 days below the tillage and straw incorporation layer.

17

A controlled, replicated experiment in 1989-1995 on loam-silt loam in British Columbia, Canada (Lupwayi et al. 2001) found higher bacterial diversity under conventional tillage (4.04 H1(Shannon diversity index) and 3.94 H1) than zero tillage (3.91and 3.84 H1 at Rolla and Dawson Creek respectively), during barley Hordeum vulgare planting time. Diversity was higher under zero tillage (3.87 and 3.76 H1) than conventional tillage (3.37 and 3.17 H1 at Rolla and Dawson Creek respectively) during barley harvesting time. There were two sites under continuous barley from 1987 to 1988 then under a barley-barley-canola Brassica campestris rotation from 1989 to 1995. During the rotation phase there were two treatments: conventional tillage (control) and zero tillage. There were four replicates at each site. Soils were sampled during the second barley phase of the rotation in 1995 to 5 cm depth.

18

A controlled, replicated experiment in 1998-2001 on a clay soil in Sweden (Djodjic et al. 2002) found that higher average phosphorus levels were found in soil under the no-tillage treatment (1.86 kg/ha) compared to conventional tillage (1.59 kg/ha) and conventional tillage plus incorporation of phosphorus fertilizer (1.25 kg/ha). There was no major effect of tillage compared with no-tillage treatments on phosphorus filtration through the soil. Large columns of soil (monoliths) were collected and exposed to three treatments: conventional tillage (five replicates), no-tillage (five replicates), and phosphorus fertilizer incorporation (three replicates). All liquid draining from the monoliths was collected, and the concentrations of soil phosphorus and dissolved phosphorus were measured.

19

A site comparison study in 1995-1997 of compaction on a loamy silt soil in Lower Saxony, Germany (Langmaack et al. 2002), found that neither of the two earthworm species studied were affected by changes in tillage. Lumbricus terrestris was not affected by compaction.Compared to uncompacted soil, burrows made by earthworm species Aporrectodea caliginosa were still lower in length (9 mm/g/day), volume (68 mm3/g/day), and windiness (17%) two years later due to the compaction event. One part of the field was compacted six times in spring 1995 by repeated wheeling by heavy four-wheel-drive machinery with a 5 Mg wheel load, the other part was uncompacted. Undisturbed soil monoliths were taken from fields in 1997 under conventional tillage or conservation tillage. X-ray computed 2D images were used to analyse soil structure.

20

A replicated controlled experiment in 2000 on a non-chalky clay soil in Bhopal, India (Bandyopadhyay et al. 2003) found thatsub-soiling in a soybean Glycine max - linseed Linum usitatissimum system reduced the size of soil cracks (12.5% in width, 10% depth, 5% length and 12% surface area) compared to conventional tillage. In a soybean-wheat Triticum aestivum rotation the smallest cracks were in mouldboard (0.014 m) compared with reduced (0.025 m) and no tillage plots (0.022 m). There were two experiments: (1) soybean /wheat rotation, with no-, reduced, mouldboard (wheat residue incorporated), and conventional tillage (wheat residue removed). There were three replications on 45 x 16 m plots, inorganic fertilizers were applied; (2) soybean/linseed rotation. This was under conventional tillage or sub-soiling (deep tillage). There were three replications 8 x 5 m, and three fertilizer treatments: no fertilizer, inorganic fertilizer, inorganic fertilizer plus farm yard manure. Crack length, depth and width, and the soil water content and density were measured.

21

Two replicated, randomized, controlled experiments from 1987 to 1998 on a clay soil in Settat, Morocco (Bessam & Mrabet, 2003) found that there was an increase in soil organic carbon in no tillage systems (by 3.5 t/ha after 4 years, and by 3.4 t/ha after 11 years) compared to conventional tillage. Nitrogen slightly decreased under both tillage practices, however the no-tillage soils contained more nitrogen than the conventionally tilled soils in both experiments. Two long-term experiments were started in 1987 and 1994. Wheat Triticum aestivum, wheat-fallow, wheat-corn Zea mays-fallow, wheat-lentils Lens culinaris-fallow and wheat-forage fallow rotations were investigated in both experiments. There were three replicates in each experiment and experimental plots were 6 x 30 m. Tillage treatments included no-tillage and conventional tillage using disc harrows. Soil samples were collected from unwheeled areas after harvest in 1998. Soil organic carbon and total nitrogen were measured.

22

A controlled, replicated experiment in 1994-1996 on clay in Brazil (Cogo et al. 2003) found the lowest soil loss under crops with no-till (1 t/ha), followed by crops under reduced tillage (4 t/ha) compared to conventional ploughing with crops (13 t/ha) and conventional ploughing on bare soil (80 Mg/ha in one crop cycle). Water losses were very low with no difference between treatments. On slopes 0.035, 0.065 and 0.095 m/m-1 gradient, the following treatments were applied after harvest of soybean Glycine max and black oat Avena strigosa crops: conventional tillage (20 cm depth), reduced tillage (8 cm depth), and no-till. There was an additional bare soil treatment under conventional tillage. Plots were 24 x 50 m and replicated three times. Tillage and planting operations were performed along contour lines in all plots except one where ploughing/disking operations were performed up-and-down-slope. Rain gauges were installed to measure runoff.

23

A controlled replicated experiment in 2000-2002 on a silt loam soil in California, USA (Jackson et al. 2003) found that tillage decreased soil quality, increasing greenhouse gas emissions and potential nitrate loss. Carbon dioxide lost from soil was highest in disked soil (39 mgCO2 m2/h) immediately after tillage. When irrigated, highest carbon dioxide loss was from no-till soil (161 mgCO2 m2/h). Nitrate levels were consistently higher in tilled than no-till soil. Two weeks after tillage, tilled soils held twice as much nitrate as no-till (12 μg NO3-N/g and 6 μg NO3-N/g respectively). Nitrogen loss from tilled soil was consistently higher in tilled than no-till soil. Tillage caused immediate changes in soil microbial community structure. There were three treatments (rototilled, disk, and no-till control), replicated three times (field scale, but area not specified). Soil cores from each replication were taken over eight sampling times. Soil carbon and nitrogen were measured. Microbial community structure was described.

24

A replicated study over a 22 year period on loamy soil in western France (Lamandé et al. 2003) showed that conventional tillage reduces both earthworm abundance (22 individuals/m2) and functional diversity (four species), whereas occasional tillage (4-yr rotation) only reduces earthworm abundance (60 individuals/m2, six species). The study comprised 3 treatments, established in plots 9 × 16 m in size: continuous maize treated with pig slurry for 22 years; the pasture phase of a rye-grass / maize rotation, also treated with pig slurry for 22 years; pasture sown with white clover and rye-grass, maintained for 9 years. Three replicate samples of the earthworm community were sampled from each treatment.

25

A controlled; randomized, replicated experiment in 2000-2001 on fine sandy-silty loam in the USA (Motavalli et al. 2003) found lower soil penetration resistance when soil was subsoiled (1.97 MPa) compared to compacted soil (3.43 MPa) and the control (3.06 MPa). There were no effects of compaction or subsoiling on inorganic nitrogen levels in 2000. In 2001, inorganic nitrogen levels were lower in the subsoiled (17.5 mg N/kg) compared to compacted (44.5 mg N/kg) or control treatments (42.5 mg N/kg). The highest corn Zea mays yield was under subsoiling (7994 kg/ha) then the control (7232 kg/ha) and compacted treatments (5411 kg/ha). Corn was planted in 3.8 x 10.6 m plots. Treatments consisted of: deep tillage to 30 cm depth (subsoiling), and three levels of soil compaction (0, 2 and 4 passes with a vibrating roller). Four rates of composted poultry manure (at 0, 6, 11, and 18 Mg/ha) were applied in spring to the deep tillage and compaction treatments. All treatments were then disced twice to 15 cm depth. There were four replications. Soils were sampled to 40 cm depth.

26

A replicated, randomized experiment in 2000-2004 on silty-clay soil in Cordoba, Spain (Gómez et al. 2004) found that no-tilled plots lost the most soil (8.5 t ha/yr), compared to those under conventional tillage (4.0 t h/yr) and grass cover (1.2 t ha/yr). There were three soil management systems: no-tillage (soil kept weed-free with herbicides), conventional tillage (3-4 passes with rotary tiller 15cm deep), grass cover (rotary tilled to 10 cm, then barley Hordeum vulgare until April, residue retained once cut). Each experimental plot was 6 x 12 m and enclosed two olive Olea europaea trees. Water runoff and sediment were measured. Soil samples up to 5 cm depth were taken from each plot. Soil organic matter, density and moisture were measured.

27

A replicated experiment from 1988 to 1998 on a loamy-sandy loam soil in Woburn, England (Quinton & Catt, 2004) found that there were no major differences in soil loss between minimal and standard tillage treatments. Soil loss was lower on across-slope plots (148 kg/ha) compared to up-and-downslope plots (262 kg/ha). Runoff was also lower in across- (0.82 mm) than up-and-downslope plots (1.32 mm). Crop yields were higher on across-slop plots than on the up-and-downslope plots, in 10 of 11 years tested. The experimental crop was a potato Solanum tuberosum/barley Hordeum vulgare/wheat Triticum aestivum/sugar beet Beta vulgaris/fallow (not specified) rotation. The main treatments were cultivation direction (up-and-downslope, across-slope) and tillage (minimal with some residue retention, conventional mouldboard ploughing with all residue removed). There were two replicates of four 25 x 35 m plots. Soil loss, runoff and yield were measured.

28

A replicated site comparison study in 1993-1995 on a silty soil in Kedainiai, Lithuania (Slepetiene & Slepetys, 2005) found that soil organic matter content in the topsoil was higher in minimally-tilled soils (1.46 g/kg) compared to shallow (1.04 g/kg) and conventionally tilled soils (0.97g/kg). There were two long-term tillage experiments, one with high application rates of mineral fertilizers (experiment one: N30-45P45K60), and the other with low application rates (experiment two: N60P90K90-120). Both experiments received mineral fertilizers and farmyard manure. There were four replicates and each area was 36 m2. The crops included vetch Vicia sativa-oat Avena sativa rotation and sugar beet Beta vulgaris. Soil sampling was done annually up to 30 cm in depth in 1993-1995. Soil nitrogen and phosphorus were measured.

A replicated experiment in 2005 on sandy loam in El Batán, Mexico (Govaerts et al. 2007) found that the rate at which microbes used carbon (metabolic activity) was higher when under conventional tillage with residue retention compared to zero tillage with residue removal, in maize. Soil microbial biomass was higher in wheat Triticum aestivum (369 mg C/kg) compared to maize Zea mays (319 mg C/kg). There were two tillage treatments: zero and conventional tillage. Within these were two residue treatments; removed or retained. Within these were maize and wheat crops, which were fertilized at 120 kgN/ha. Crop rotation plots (continuous wheat/maize, wheat and maize) were 7.5 x 22 m. There were two replications. Soil samples were collected to 15 cm depth from all plots. Total nitrogen and organic carbon were measured.

A replicated experiment in 1994-1999, on clay soil in Queensland, Australia (Li et al. 2007), found that water infiltration and yield were higher in plots using conservation tillage. Controlled traffic combined with zero tillage reduced runoff by 47.2 % and increased yield by 14.5 %. The 90 m2 tillage plots were arranged in pairs: one plot had zero tillage and the other stubble mulch tillage, within which were two traffic treatments: non-wheeled and wheeled. This was replicated four times. Compacted areas were wheeled annually using a 100 kW tractor. Crops included: wheat Triticum aestivum, sorghum Sorghum bicolor, maize Zea mays, sunflower Helianthus annus and sweet corn (different cultivar of maize). Yield was determined from harvested transects in the plots. Runoff and soil moisture content was measured by taking soil cores between 0-50 mm depth and measuring moisture content gravimetrically. Controlled traffic and zero tillage combined were not separated in results.

34

A randomized, paired experiment in 2004 on loamy soil in Essonne, France (Limousin & Tessier, 2007) found that soil organic carbon levels were 11.4% higher in soil under no-tillage than under conventional tillage management. No-tilled soils also contained more potassium (3.5-11% compared to 3-4.5%). No effects on yield were found between conventional and no-tillage management. No-tillage management showed strong pH gradients depending on soil depth, but ploughed soil had an even pH. The experimental field was divided into two 50 x 16 m plots, which were subjected to either conventional or no-tillage treatment. The crops grown were maize Zea mays followed by wheat Triticum aestivum. Maize/wheat plantings received similar fertilizers. Soil samples were taken from three random locations within each tillage treatment. Organic carbon, potassium and soil pH were measured. To measure the density of the soil, five soil samples were taken from five random locations in each tillage treatment.

35

A replicated study in 2001-2006 on a silty-clay soil in Lower Saxony, Germany (Koch et al. 2008) found that adopting mouldboard ploughing reduced soil penetration resistance (0.5-1.0 MPa) compared to shallow tillage (1.5 MPa). Soil porosity under shallow tillage changed depending on the soil depth, but was uniform at all depths when under mouldboard ploughing. Shallow tillage reduced sugar beet yield (15 Mg/dm/ha) compared to mouldboard ploughing (19 Mg/dm/ha). Sugar beet Beta vulgaris was planted at a density of about 90,000 plants/ha in three adjacent fields. Cultivation of crops under shallow tillage or mouldboard ploughing followed regional standards of good professional practice. Soil penetration resistance was measured to 0.65 m depth in spring. After sugar beet sowing, undisturbed and disturbed soil core samples were taken in spring 2004-2006, from 0.05m to 0.6 m depth.

36

A randomized, replicated experiment from 1997-2002 on silty soil in China (Wang et al.2008) found 22% higher soil organic matter, 51% higher total nitrogen and 97% more phosphorus under no-tillage with straw cover compared to conventional tillage with straw removed. Soil microbial carbon and nitrogen increased by 135% and 104% and wheat Triticum aestivum yield by 16% under no-tillage straw cover, compared to conventional tillage with straw removed. The effects of tillage and residue retention were not separated. There were two treatments in a wheat crop: no tillage with straw cover (standing stubble retained and all wheat straw was left as mulch cover (3.8 t/ha), and conventional tillage with straw removed (tillage to 15 cm depth twice, majority of straw removed (0.7 t/ha remaining)). Fertilizer, herbicide and insecticide application was the same for both treatments. There were three replicates of each treatment. Each plot was 9 x 78 m. Soils were sampled in 2007 up to 30 cm depth.

37

A controlled experiment in 2003-2004 on silty clay loam soil in Peñaflor, Spain (Álvaro-Fuentes et al. 2009) found that soil organic carbon was more than 30% higher in topsoil under no-tillage (853 g/m2 continuous barley, 671 g/m2 barley-fallow) compared to conventional tillage (547 g/m2 continuous barley, 490 g/m2 barley-fallow). Organic carbon levels in large aggregated soil particles was greater under no-tillage (4.1 g C/kg) than conventional tillage (1.2 g C/kg) in continuous barley, indicating improved soil structure, but did not differ in the barley/fallow rotation. Three tillage systems (no-tillage with a direct driller and herbicide treatment, reduced tillage with a chisel plough to 30 cm, conventional tillage with a mouldboard plough to 35 cm and a pass with a tractor-mounted scrubber), contained two cropping systems: barley Hordeum vulgare/fallow rotation, continuous barley. In each plot, 12 soil cores were taken to 20 cm depth (size/number of plots not specified). Total soil organic carbon was measured.

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A before-and-after trial in 2003-2005 on a loam - sandy loam soil in Scotland, UK (Ball & Crawford, 2009), found that mechanical weeding caused structural deterioration and subsoil compaction under broad bean Vicia faba crops (17.5 kPa – 39 kPa with increasing depth) due to tractor wheeling. In the carrot Daucus carota crop, soil was >50 kPa for each soil type when wheeled, and <22 kPa for each soil type in unwheeled areas. Compaction control measures (controlled traffic and precision driving) are therefore important when using mechanical weeding. The broad bean crop was part of an eight year rotation of vegetables, potatoes, wheat Triticum aestivum, beans, barley Hordeum vulgare, peas Pisum sativum and red clover Trifolium pratense. The carrot crop was part of a cereal/potato/carrot/spring cereal rotation undersown with grass and clover and peas. Carrot beds were roughly 2 m wide. Soil strength and the soil density were measured. Weeds were controlled by several passes of a light spring-tine harrow in the broad bean crop, and by a steerage hoe between the rows of carrot.

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A controlled experiment in 2003-2006 on sandy loam soil near Copenhagen, Denmark (Daraghmeh et al. 2009) found that reducing tillage improved soil structure by increasing soil organic matter and reducing soil density. Soil stability was higher under reduced tillage in wet conditions (74.3% on average) compared to conventional ploughing (66.8% on average), but higher under conventional ploughing in dry conditions. This is due to higher soil organic matter content in the reduced tillage (3.06 mg/m3) compared to the conventional ploughing (2.6 mg/m3). The optimal time for tillage appears to be determined by the water content of the soil. There were two tillage treatments in an experimental field (size not specified); reduced tillage with harrowing, and convention mouldboard ploughing with harrowing. Soil samples were taken 6 times during the tillage year. Soil texture, organic matter, stability and density were measured.

A replicated experiment in 2001-2006 on loam soil in Saskatchewan, Canada (Malhi et al. 2009), found that reducing tillage intensity increased soil stability, due to increased crop residue cover (50% cover in the reduced input treatment, compared to 24% in organic and 30% in high input treatments). Excess soil nitrogen was stored as soil organic matter in dry weather, largely due to reduced tillage. Three input levels were replicated four times: organic (organic management under conventional tillage), reduced (combined pest and nutrient management under no tillage) and high (recommended fertilizer and pesticide application under conventional tillage) inputs (treatment size not specified). At the end of each growing season 36 soil samples were taken from each input treatment, with an additional 18 taken in 2006. Soil stability, organic carbon and crop residue cover were measured.

42

A randomized, replicated experiment in 2008 on fine sandy loam soil in Spain (Moreno et al. 2009) found greater soil organic carbon levels in tilled soil (9.94 g C/kg) and soil with a mown cover crop (9.91 g C/kg) than soil with no cover crop (5.36 g C/kg). Bacteria counts under tillage were lower (233 million/g soil) than under mown cover crops (952 million/g soil) or cover crops plus herbicide (1.4 billion/g soil), but were higher than in the no cover crop (32 million/g soil). There were four long-term treatments in an olive Olea europaea orchard: tillage (3-4 passes with disk harrow to 30 cm depth, tine harrow in summer); no-till and no cover (treated with glyphosate herbicide); cover crop plus herbicide (treated in March); cover crops plus mower (herbicide-free). Each plot was 11 x 11 m and consisted of 16 trees. Each treatment was replicated four times. Two soil samples were taken from the centre of each plot. Soil bacterial numbers and community structure were measured.

A randomized, replicated experiment in 2004 on a fine sandy-loam soil in North Carolina, USA (Overstreet et al. 2010) found nematode numbers were 48% higher and earthworm numbers were 31 times higher under strip tillage compared to conventional tillage. Nematode numbers were more than four times higher in organic strip tillage plots compared to conventional tillage plots receiving synthetic chemicals. Nematode and earthworm numbers were up to four times and 30 times higher respectively in plots where strip tillage and organic inputs were combined. There were four treatments: strip tillage with organic inputs (soybean Glycine max meal fertilizer and pesticide), strip tillage with synthetic inputs (ammonium nitrate at 200 kg/ha), conventional tillage with organic inputs and conventional tillage with synthetic inputs. There were four replications. The study took nematode samples and earthworm extractions (species not specified for either group).

A replicated study in 2005, carried out in greenhouses and field conditions (soil type not specified) at the University of Évora, Portugal (Brito et al. 2011) found that no-till cultivation techniques were effective in maintaining the abundance (proportion of colonization: 0.14 and 0.03 for no-till and conventional tillage respectively) and diversity of arbuscular mycorrhizal fungi in the soil of a wheat crop Triticum aestivum during Mediterranean summer conditions. Experimental treatments were established in 42 pots, corresponding to seven replicates of two treatments, under greenhouse conditions. Pots were then buried in the field and subjected to typical Mediterranean temperature and rainfall regimes.

47

A randomized, replicated experiment from 1968 to 2008 on clay soil in Queensland, Australia (Dalal et al. 2011) found higher soil organic carbon under no-tillage (20.21 Mg/ha) compared with conventional tillage (19.83 Mg/ha). Total soil nitrogen was not affected by tillage treatment. Average grain yield was highest under no-tillage when crop residue was retained (2.86 Mg/ha) with high fertilizer application, and lowest under conventional tillage when crop residue was retained (2.28 Mg/ha) with no fertilizer. This 40- year experiment was cropped with wheat Triticum aestivum except for three years which were cropped with barley Hordeum vulgare and had the following treatments: tillage (conventional tillage (3-4 times to 10 cm depth), no-tillage); crop residue management (residue burned, residue retained); and nitrogen fertilizer application (none applied, 30 kg N/ha/year (low), and 90 kg N/ha/year (high), applied at sowing). Plots were 61.9 x 6.4 m and were replicated four times. Five soil samples were taken from each plot at the end of the experiment (May 2008) to 1.5 m depth.

48

A randomized, replicated experiment in 2004-2005 on sandy soil in Portugal (de Varennes & Torres, 2011) found higher soil organic carbon (5.75 g C/kg), extractable phosphorus (57.75 mg P/kg) and number of fungal colonies (0.003 colonies/g soil) under no-tillage compared to conventional tillage (6.45 g C/kg, 65.5 mg P/kg and 0.004 colonies/g soil respectively). Mineral nitrogen remained the same over the two years of the experiment. Tillage treatment had no effect on overall grain yield for lupin (1.2 t/ha dry weight) or oat (4.2 t/ha dry weight). There were two treatments in 400 m2 plots: conventional tillage (two passes with a disc plough to 15cm), and no-till (left undisturbed). Each tillage treatment was divided into six 5 x 10 m plots. Three were sown with lupin and three with oat. Soils were sampled to 15 cm depth six times each year during the experiment.

A controlled, replicated experiment in 2005-2009 on silty loam soil in eastern Spain (García-Orenes et al. 2012) found that after five years, conventional ploughing gave the lowest levels of soil organic matter (2%), arbuscular mycorrhizal proteins (400 mg/g soil), aggregate stability (57%), and higher soil erosion rates (0.01 Mg/ha/h) compared to soil under native vegetation. Ploughing plus sown oats had similar values to conventional ploughing. All treatments without ploughing had similar values to the control (2.7% organic matter, 696 mg/g soil, 57.4% aggregate stability and 0.01 Mg/ha/hour respectively). There were three replicates of five management treatments including: ploughing (four times/year to 20 cm depth), ploughing (as before) then sowing oats, herbicide application (three times/year) and no ploughing, addition of oat straw mulch and no ploughing, and land abandonment (control). Plots were 6 x 10 m. Soil under native vegetation was used as a reference. Six soil samples from each plot were taken annually to 5 cm depth. Five rainfall simulations were also conducted during the summer drought period on 1 m2 plots to test for soil erosion. Simulations lasted one hour at 55 mm/h.

52

A controlled, randomized, replicated experiment in 2007-2010 on sandy silt-loam in India (Ghosh et al. 2012) found that soil loss and runoff were lower under minimal tillage with palmarosa Cymbopogon martini (3.4 t/ha and 234 mm, respectively), than with no vegetation barrier (7.1 t/ha, 428 mm). Conventional tillage with panicum was less effective (5.2 t/ha, 356 mm) than conventional tillage with palmarosa. Maize Zea mays yield was 43% higher under minimal tillage with palmarosa compared to no vegetation barrier with conventional tillage. The succeeding wheat Triticum aestivum yield was on average 73% higher in the palmarosa relative to panicum treatment, and 99% higher than with no vegetation barrier. It was not clear whether these results were due to organic amendments, mulching or reduced tillage. There were three replications of three treatments in a maize-wheat crop rotation: conventional tillage with no vegetation barrier but applying fertilizers and herbicides; conventional tillage with a panicum Panicum maximum vegetation barrier, fertilizers and herbicides; minimal tillage (30% crop cover retained) with a palmarosa vegetation barrier plus mulching and farmyard manure, vermicompost (produced by worms) and poultry manure applications. Plots were 100 x 20 m.

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A replicated experiment in 2009 on chalky soils in Valencia, Spain (González-Peñaloza et al. 2012) found that slight water repellency (a property that influences the movement of water into the soil) was found in no-till soils with added manure and plant residues (0-65 s wettable soil, >60 is strongly water repellent), compared to conventional tillage where the soils remained wettable (0 s wettable soil). This was due to the higher levels of soil organic carbon in the no-till (2.3-8.3% organic matter) compared to conventionally tilled plots (1.2-2.4% organic matter). There were four replications of citrus-cropped soil plots (species and plot size not specified). Within the crop, the treatments were: no-tillage with plant residues, organic manure and no chemical fertilizer; no-tillage and conventional herbicides; conventional tillage. Water repellency and soil organic carbon were measured.

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A replicated, randomized, controlled trial between 2006 and 2009 in a clay loam soil in Hubei Province, China (Li et al. 2012) found that soil organic carbon in the top 5 cm of the soil was increased under: no tillage for rape Brassica napus but tillage for rice Oryza sativa (by 6 %), continuous no tillage (by 9%), and continuous no tillage with a mulch of crop residues (by 17%), relative to full tillage. The trial used four crop rotation and tillage treatments: , rape and rice with full tillage, rape and rice with continuous no tillage, rape without but ricewith tillage, and rape and rice without tillage but with mulches. Tillage plots were tilled by hand to 10 cm depth then mouldboard ploughed to 30 cm depth. Rape and rice were harvested in May and October each year, and residues were air dried before being left on the soil surface in the mulching treatment.

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A replicated experiment in 2004-2006 on silty soils in Germany (Andruschkewitsch et al. 2013) found that soil organic carbon was higher in no-tillage (11.6 g/kg soil) and mulch tillage (12.3 g/kg soil) than conventional tillage (10.1 g/kg soil). Results were similar across all sites. Yields of sugar beet Beta vulgaris and winter wheat Triticum aestivum were higher under conventional (72.7 t/ha, 8 t/ha) and mulch tillage (69.7 t/ha, 8 t/ha) than no-tillage (62.8 t/ha, 7.5 t/ha respectively). There were four replicates (sites). Sugar beet was followed by two years of winter wheat as crop rotations. At each site, one field was chosen and divided into three plots (size not specified). Each plot had a different tillage treatment: conventional tillage (25-30 cm deep), mulch tillage (10-15 cm), no-tillage. In 2010, 15 soil samples were taken from each treatment. Soil organic carbon and nitrogen were measured. Yields were measured annually from 2004 to 2010.

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A randomized, experiment in 2010 on sandy loam soil in north-east Spain (Plaza-Bonilla et al. 2013) found that soil organic carbon levels were highest in soils which had been managed under no-till for 11 years (ranging from 7.1 to 24 g C/kg dry soil) compared to no-till for one year (8.9-10.5 g C/kg dry soil) and four years (8.5-20 g C/kg dry soil) respectively. The experimental field was 7500 m2, and had previously been intensively tilled. Two crops (either wheat Triticum aestivum or barley Hordeum vulgare) were exposed to one of five treatments: conventional tillage (mouldboard plough, 1500 m2), no-till for one year, no-till for four years, no-till for 11 years, no-till for 20 years (the remaining 6000 m2). Pig slurry was applied across the whole experiment as fertilizer. From each treatment, three soil samples were taken in 2010 after crop harvest. Soil organic carbon levels were measured.

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